The present invention relates to a method of forming micropatterns in the process of fabricating semiconductor integrated-circuit devices or the like.
In a conventional process of manufacturing ICs or LSIs, patterns are generally formed by photolithography using an ultraviolet ray. With the miniaturization of semiconductor devices, however, a light source of a shorter wavelength has been used increasingly. As a resist compatible with the light source of a shorter wavelength, there has been used a chemical amplification resist which provides high sensitivity as well as high resolution (e.g., O. NALAMASU et. al., Proc. SPIE, 1262, 32(1990)).
The chemical amplification resist is a multi-component resist containing an acid generator which generates an acid in response to the radiation of an energy beam and a compound which reacts with the acid. Among polymers which react with an acid, a compound with the structure as shown in the following [Formula 1] is known. ##STR1## where R is an alkoxycarbonyl, alkyl, alkoxyalkyl, alkylsilyl, tetrahydropyranyl, alkoxycarbonylmethyl, or like group, which is easily decomposed by an acid. Such a chemical amplification resist contains, as its main component, a polymer which presents a low absorption index with respect to light in the range of shorter wavelengths, such as a derivative of polyvinyl phenol. Accordingly, the transparency of the chemical amplification resist is increased and the reaction of the resist proceeds through a chain reaction induced by an acid catalyst, resulting in high sensitivity and high resolution. Hence, the chemical amplification resist is considered as a promising material for forming micropatterns by utilizing a light source of a shorter wavelength.
At present, a vigorous study is being directed to the formation of a resist pattern of 0.2 .mu.m or less in size in accordance with a deep-ultraviolet-ray exposure method using such a chemical amplification resist. However, since the aspect ratio of a resist pattern becomes higher with the increasing miniaturization thereof, a conventional wet developing method is disadvantageous for the following reason. Specifically, a resist film coated on a semiconductor substrate is exposed to a deep ultraviolet ray and then developed, resulting in a resist pattern. After that, a developing solution and the resist material dissolved in the developing solution are washed away from the resist pattern with pure water. Finally, the resist pattern is subjected to spin drying, which involves the rotation of the resist pattern at a high speed.
In the step of drying the resist pattern, however, large surface tension acts on pure water 82 remaining between adjacent resist patterns 81 formed on that region of a semiconductor substrate 80 having a high aspect ratio, as shown in FIG. 16(a). As a result, the resist patterns 81 are distorted or broken by the large surface tension exerted thereon, thereby causing a phenomenon that the resist patterns are leaning against their adjacent resist patterns, as shown in FIGS. 16(b) and 16(c). The phenomenon is similarly observed in the case of using a normal resist, instead of using the chemical amplification resist.
To eliminate the disadvantage, there has been proposed a method for forming a resist pattern by performing dry etching with respect to a resist film of chemical amplification type, as disclosed in U.S. Pat. No. 5,278,029. Below, a description will be given to the method with reference to FIGS. 17(a) and 17(b) and to FIGS. 18(a) and 18(b).
Initially, as shown in FIG. 17(a), a resist film 91 of chemical amplification type coated on a semiconductor substrate 90 is irradiated with KrF excimer laser light 93 through a mask 92, thereby generating an acid in an exposed portion 91a of the resist film 91. The exposed portion 91a is made hydrophilic by the action of the resulting acid and hence is apt to absorb water in the atmosphere. Consequently, a thin absorption layer 94 of water is naturally formed on the surface of the exposed portion 91a.
Subsequently, an alkoxysilane gas is introduced into the surface of the resist film 91, thereby forming an oxide film 95 on the surface of the exposed portion 91a, as shown in FIG. 18(a). Thereafter, dry etching by RIE using an O.sub.2 plasma 96 is performed with respect to the resist film 91 through the oxide film 95 as a mask, thereby forming a minuscule resist pattern 97, as shown in FIG. 18(b).
However, the resist pattern actually formed in accordance with the above method was disadvantageous in that the oxide film 95 was caused to flow in a step of evaporating an alcohol, resulting in an increased degree of edge roughness of the oxide film 95, which deteriorates the size precision of the resist pattern. As a result of diagnostic examination, the deformation of the oxide film 95 was attributed to the thinness of the oxide film 95.